1. Field of the Invention
This invention relates to a method for plasma treatment and an apparatus for plasma treatment, and more particularly to a method for plasma treatment including an operation of detecting particles contained in the plasma used for growing or etching a membrane and an apparatus for plasma treatment possessed of a mechanism for the detection of such particles.
2. Description of the Prior Art
The process for producing a semiconductor device, for example, includes a step for forming a membrane, for example film, such as is used for a semiconductor, insulator, or conductor by the method of plasma vapor phase deposition or etching such membrane by the reactive ion etching method, plasma etching method, etc. The construction for generating plasma in this process is known in various types, i.e. a construction adapted to apply radio frequency power to a pair of electrodes installed in a reduced-pressure atmosphere, a structure adapted to apply high-frequency power to a conductive coil disposed around a plasma generating zone, and a construction adapted to introduce a microwave into a plasma generating zone from an external source.
The problem which is raised during the generation of such plasma resides in the fact that the particles (suspended fine particles) which are present in the plasma mingle into a membrane in the process of deposition or adhere to a membrane in the process of patterning and impair the pattern conferred on the finished membrane.
These particles are mainly produced by the emission from a sputtered membrane or by the accidental bombardment of the plasma by the clusters shed from the inner wall of the chamber.
The clusters scattered from the inner wall of the chamber roughly measure some tens of nm across. In the plasma, they either agglomerate electrostatically or constitute themselves the seeds for growth of a reactive radical element, with the result that they will eventually form particles and settle down.
Various methods, therefore, have been employed in an effort to determine the condition of occurrence of such particles in the plasma. The surveillance of particles by means of a CCD camera is disclosed in JP-A-06-124,902 and JP-A-07-142,410, the method resorting to the practice of taking count of particles passing through an exhaust line is disclosed in JP-A-03-226,579, and the procedure comprising the steps of collecting particles and taking count of them by means of a detector is disclosed in JP-A06-123,693, for example.
For the observation of particles by the CCD camera, the existing level of CCD resolution does not allow fully accurate determination. The method of taking count of particles passing through the exhaust line or the method of collecting and taking count of particles encounters difficulty in acquiring real-time determination of the occurrence of particles with high accuracy.
As a means of effecting field observation of the number of particles, an optical method resorting to the laser scattering process is disclosed, for example, in T. Kamata et al., Plasma Sources Sci. Technol. 3, 1994, pp. 310-313. This method consists in detecting the Mie scattering light generated by particles with the aid of an optical detector.
The apparatus used for this detection of particles is constructed as illustrated in FIGS. 19A and 3, for example. Specifically, it has a Argon Ion laser 1 for injecting a laser beam in a plasma zone A, an optical detector 2 for admitting the Mie scattering light caused by particles, a rotary polarizer 3, and a lens 4 arranged accordingly.
When the laser beam is incident on the particles in the plasma zone A causes the Mie scattering light, the light passes through the rotary polarizer 3, and is collimated into the optical detector 2 by the lens 4.
The rotary polarizer 3 converts the incident light to the linear polarization light and injects the linear polarized light into the optical detector 2. Let the plane including both laser beam and direction of scattered light of the linear polarized light serve as a plane of observation, and the beam of light parallel to the plane of observation will form a P polarized light component and the beam of light perpendicular to the plane of observation will form an S polarized light component. Then, the size of particles of interest is rated by the magnitude of the division S/P.
With reference to FIG. 19A, reference numeral 10 denotes an apparatus for plasma treatment, 11 a chamber, 13, a first electrode, 14 a second electrode, 17 a capacitor, 18 a high-frequency power source, 20 a window pervious to light, and 22 an air vent.
With the mechanism for detecting such particles by the use of the laser scattering method described above, it is difficult to attain additional installation of an optical detector and a light source within the existing chamber which is possessed of a plasma zone.
Moreover, since the Mie scattering light is unusually feeble and rich in optical noise, any apparatus which is capable of accurately detecting this light is complicated in mechanism and expensive as well.